See-through eyepiece for head wearable display

ABSTRACT

An eyepiece for a head wearable display includes a light guide component for guiding display light received at a peripheral location and emitting the display light at a viewing region. The light guide component includes an eye-ward facing surface having a reflection portion and a viewing portion, a folding surface oriented to reflect the display light received into the light guide component to the reflection portion of the eye-ward facing surface, and a first interface surface oriented to receive the display light reflected from the reflection portion of the eye-ward facing surface. A partially reflective layer is disposed on the first interface surface in the viewing region to reflect the display light through viewing portion of the eye-ward facing surface.

CROSS REFERENCE TO RELATED APPLICATION

The present patent application is a continuation of U.S. applicationSer. No. 14/135,284 filed on Dec. 19, 2013, the contents of which areincorporated herein by reference.

TECHNICAL FIELD

This disclosure relates generally to the field of optics, and inparticular but not exclusively, relates to eyepieces for head wearabledisplays.

BACKGROUND INFORMATION

A head mounted display (“HMD”) or head wearable display is a displaydevice worn on or about the head. HMDs usually incorporate some sort ofnear-to-eye optical system to create a magnified virtual image placed afew meters in front of the user. Single eye displays are referred to asmonocular HMDs while dual eye displays are referred to as binocularHMDs. Some HMDs display only a computer generated image (“CGI”), whileother types of HMDs are capable of superimposing CGI over a real-worldview. This latter type of HMD typically includes some form ofsee-through eyepiece and can serve as the hardware platform forrealizing augmented reality. With augmented reality the viewer's imageof the world is augmented with an overlaying CGI, also referred to as aheads-up display (“HUD”).

HMDs have numerous practical and leisure applications. Aerospaceapplications permit a pilot to see vital flight control informationwithout taking their eye off the flight path. Public safety applicationsinclude tactical displays of maps and thermal imaging. Other applicationfields include video games, transportation, and telecommunications.There is certain to be new found practical and leisure applications asthe technology evolves; however, many of these applications are limiteddue to the cost, size, weight, field of view, and efficiency ofconventional optical systems used to implemented existing HMDs.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating the principles beingdescribed.

FIG. 1A is a plan view illustration of a see-through eyepiece for a headwearable display, in accordance with an embodiment of the disclosure.

FIG. 1B illustrates a curved wedge portion of a see-through eyepiece fora head wearable display, in accordance with an embodiment of thedisclosure.

FIG. 2 is a perspective illustration of a see-through eyepiece for ahead wearable display, in accordance with an embodiment of thedisclosure.

FIG. 3 is a plan view illustration of a see-through eyepiece including aframe mount, in accordance with an embodiment of the disclosure.

FIGS. 4A and 4B illustrate a demonstrative head wearable displayincluding a see-through eyepiece, in accordance with an embodiment ofthe disclosure.

FIGS. 5A & 5B are appendixes that provide sag equations describingsurface curvatures of a demonstrative implementation of a see-througheyepiece, in accordance with an embodiment of the disclosure.

DETAILED DESCRIPTION

Embodiments of a system and apparatus for a see-through eyepiece of ahead wearable display are described herein. In the following descriptionnumerous specific details are set forth to provide a thoroughunderstanding of the embodiments. One skilled in the relevant art willrecognize, however, that the techniques described herein can bepracticed without one or more of the specific details, or with othermethods, components, materials, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring certain aspects.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

FIGS. 1A, 2, and 3 illustrates a see-through eyepiece 100 for use with ahead wearable display, in accordance with an embodiment of thedisclosure. FIG. 1A is a plan view of eyepiece 100, FIG. 2 is aperspective view of eyepiece 100, and FIG. 3 is another plan viewincluding a frame mount. The illustrated embodiment of eyepiece 100includes a light guide component 105, a see-through add-on component110, a partially reflective layer 115, a display source 120, and a framemount 125. FIG. 1B illustrates just the see-though add-on component 110and partially reflective layer 115. The illustrated embodiment of lightguide component 105 includes an input surface 130, an eye-ward facingsurface 135, a folding surface 140, an interface surface 145, and aviewing region 147. The illustrated embodiment of add-on component 110includes an interface surface 150 and an external scene facing surface155. Eye-ward facing surface 135 includes a reflective portion 160 and aviewing portion 165. Viewing region 147 is a volumetric region ofeyepiece 100 in front of eye 175, while viewing portion 165 is a portionof eye-ward facing surface 135 where display light 180 and externalscene light 170 pass through to eye 175.

In one embodiment, light guide component 105 and add-on component 110are fabricated as two independent pieces that are bonded together alonginterface surfaces 145 and 150 using a clear adhesive. Light guidecomponent 105 and add-on component 110 may be fabricated of twodifferent materials having the same index of refraction, or both of thesame material. For example, light guide component 105 and add-oncomponent 110 may be fabricated of optical grade plastic (e.g., ZeonexE-330-R), glass, or otherwise. In one embodiment, the components areinjection molded to shape, processed to add various opticalcoatings/layers discussed below, and then bonded together alonginterface surfaces 145 and 150. In one embodiment, light guide component105 and add-on component 110 are fabricated of a material having ahigher index of refraction than air to induce total interface refraction(“TIR”) at one or more surfaces within light guide component 105.

In the illustrated embodiment, partially reflective layer 115 isdisposed between light guide component 105 and add-on component 110along interface surfaces 145 and 150. Partially reflective layer 115 maybe coated onto one or both interface surfaces 145 and 150 prior tobonding the two components together. Partially reflective layer 115 maybe implemented as a convention beam splitter (e.g., non-polarized beamsplitter film) or a polarized beam splitter (“PBS”). The splitting ratiomay be selected according to design needs, but in one embodiment may beimplemented as a 50/50 beam splitter. In embodiments where partiallyreflective layer 115 is implemented using a PBS, display source 120would output polarized light with a polarization selected tosubstantially reflect off of partially reflective layer 115. A PBSdesign can serve to increase the efficiency of the optical system. Forexample, LCD or liquid crystal on silicon (“LCoS”) are example displaytechnologies that output polarized light. Of course, external polarizingfilms may be used in connection with other non-polarized displaytechnologies. When operating with polarized light, it can be beneficialto use low stress materials to reduce the influence of birefringence onthe optical design. Accordingly, in some embodiments, light guidecomponent 105 may be fabricated of low stress plastics, glass, or otherlow stress optical grade materials.

Since beam splitter is only partially reflective and light guidecomponent 105 and add-on component 110 are fabricated of opticallytransmissive materials (e.g., clear plastic), viewing region 147 permitsat least a portion of external scene light 170 to pass through to eye175. Eyepiece 100 operates as an optical combiner combining externalscene light 170 with display light 180 emitted through viewing portion165 along an eye-ward direction into eye 175. In this way, eyepiece 100is capable of displaying an augmented reality to eye 175.

During operation, display source 120 emits display light 180 from aperipheral location offset from viewing region 147 into light guidecomponent 105. Display source 120 may be implemented using a variety ofdifferent display technologies including a liquid crystal display(“LCD”), an organic light emitting diode (“OLED”) display, or otherwise.Display light 180 may include computer generated images.

Display light 180 is incident into light guide component 105 throughinput surface 130. Input surface 130 is a curved surface with opticalpower. In one embodiment, input surface 130 operates to magnify displaylight 180 for a near-to-eye configuration. In one embodiment, inputsurface 130 includes curvature refinements to control opticaldistortion. Surface S1 in FIG. 5A presents a sag equation withcoefficient values describing an example curvature for input surface130, in one embodiment.

After display light 180 enters into light guide component 105 throughinput surface 130, it is incident upon folding surface 140, which isdisposed adjacent to input surface 130. Folding surface 140 operates toreflect display light 140 towards reflective portion 160 of eye-wardfacing surface 135. In one embodiment, both eye-ward facing surface 135and folding surface 140 are clear surfaces that reflect display light180 via TIR and careful design control over the incident angles of thelight path followed by display light 140. By using TIR for thereflections off of folding surface 140 and eye-ward facing surface 135,eyepiece 100 achieves desirable industrial design characteristics, sinceeyepiece 100 will appear as a clear eyepiece to external observers. Inanother embodiment, folding surface 140 may be coated with a reflectingfilm to reflect display light 180 without need of TIR. Surface S2 inFIG. 5A presents a sag equation with coefficient values describing anexample curvature for folding surface 140, in one embodiment.

After folding (e.g., reflecting) display light 140 at folding surface140, display light 180 is directed towards reflective portion 160 ofeye-ward facing surface 135. Eye-ward facing surface 135 is disposedopposite to folding surface 140 in an opposing configuration. Asmentioned above, the display path angles are carefully controlled duringdesign such that the incident angle of display light 180 on reflectiveportion 160 of eye-ward facing surface 135 results in a reflection dueto TIR. Surface S3 in FIG. 5A presents a sag equation with coefficientvalues describing an example curvature for eye-ward facing surface 135,in one embodiment. Accordingly, in one embodiment, display light 180undergoes just two reflections within light guide component 105 via TIR.

Reflective portion 160 redirects display light 180 to interface surface145 in viewing region 147. Interface surface 145 is disposed oppositeeye-ward facing surface 135 in an opposing configuration, but isadjacent to folding surface 140 though it has a different curvature thanfolding surface 140. Interface surface 145 is coated with partiallyreflective layer 115, which again reflects display light 180 to viewingportion 165 of eye-ward facing surface 135. Surface S4 in FIG. 5Bpresents a sag equation with coefficient values describing an examplecurvature for interface surface 145, in one embodiment.

Display light 180 incident upon viewing portion 165 of eye-ward facingsurface 135 is incident at an angle that does not result in TIR. Assuch, display light 180 passes through eye-ward facing surface 135 inviewing portion 165 along an eye-ward direction. As is illustrated inFIG. 1A, reflective portion 160 and viewing portion 165 of eye-wardfacing surface 135 may overlap each other. These portions of eye-wardfacing surface 135 describe non-mutually exclusive portions of eye-wardfacing surface 135 where display light 180 is either reflected ortransmitted due to its incident angle and the properties of TIR.

The reflective lensing due to the combined reflections off of foldingsurface 140, eye-ward facing surface 135, and partially reflective layer115 along with the refractive lensing from input surface 130 andeye-ward facing surface 135 at viewing portion 165 combine to magnifydisplay light 180 for easy viewing in a near-to-eye configuration. Thismagnification operates to displace the virtual image further back fromthe eye (e.g., 10 m) to allow the eye to readily bring it into focus. Inone embodiment, the lensing provided by input surface 130 further servesto reduce optical distortion while the lensing provided by foldingsurface 140, eye-ward facing surface 135, and partially reflective layer115 further serves to reduce astigmatism. The lensing provided by theseoptical surfaces facilitates an image plane at display source 120 thatis flatter than 0.1 diopters and the design supports a 20% modulationtransfer function (“MTF”) at 55 cycles/mm, after design tolerances,sufficient for high definition resolutions with a 9.5 um pitch displaysource.

In one embodiment, add-on component 110 is bonded onto light guidecomponent 105 in viewing region 147. Interface surface 150 of add-oncomponent 110 is designed with a curvature that smoothly mates to thecurvature of interface surface 145 of light guide component 105.Furthermore, add-on component 110 is designed with a curved prism orcurved wedge shape that forms a smooth, continuous outer surface thatincludes folding surface 140 and external scene facing surface 155. Inone embodiment, the first, second, and third derivatives of thecurvatures of both folding surface 140 and external scene facing surface155 are controlled to achieve a smooth and continuous transition at thejunction between folding surface 140 and external scene facing surface155.

In one embodiment, add-on component 110 and light guide component 105are fabricated of material(s) having the same or similar index ofrefraction. This serves to remove optical power at the junction betweeninterface surfaces 145 and 150 for external scene light 170 that passesthrough viewing region 147 to eye 175. Additionally, the curvature ofexternal scene facing surface 155 is complementary to eye-ward facingsurface 135 to counter-act the refractive lensing of viewing portion 165of eye-ward facing surface 135. In short, the input angle of externalscene light 170 entering external scene facing surface 155 issubstantially equivalent to the output angle of external scene light 170exiting eye-ward facing surface 135. As such, eyepiece 100 passes atleast a portion of external light 170 through viewing region 147substantially without lensing, thereby permitting the user to have asubstantially undistorted view of the ambient environment in front ofeyepiece 100.

In one embodiment, the surfaces of eyepiece 100 at which the opticalpath of display light 180 is redirected via TIR are coated withanti-fingerprint coatings. For example, in one embodiment, both foldingsurface 140 and eye-ward facing surface 135 are coated with ananti-fingerprint coating to reduce the impact of fingerprint oils ontotal internal reflection at these surfaces. Anti-fingerprint coatingsare known in the art.

FIG. 2 is a perspective view of a see-through eyepiece 100 illustratinghow display source 120 may be mounted to input surface 130. In oneembodiment, light guide component 105 may include recesses 205 tofacilitate a clip on mount for attaching display source 120 to lightguide component 105. As illustrated, in one embodiment, light guidecomponent 105 and add-on component 110 have substantially rectangularcross-sectional shapes.

Eyepiece 100 is suitable for use as a compact eyepiece for a headwearable display. For example, eyepiece 100 may be suitably designedwith an 18 mm eye relief, a 16 degree diagonal field of view, a 20 mm to30 mm length for eye-ward facing surface 135, and an 8 mm to 11 mmcircular diameter eyebox. Of course, other dimensions may beimplemented.

FIGS. 4A and 4B illustrate a monocular head wearable display 400 using asee-through eyepiece 401, in accordance with an embodiment of thedisclosure. FIG. 4A is a perspective view of head wearable display 400,while FIG. 4B is a top view of the same. See-through eyepiece 401 may beimplemented with embodiments of eyepiece 100 as discussed herein. Thesee-through eyepiece 401 is mounted to a frame assembly, which includesa nose bridge 405, left ear arm 410, and right ear arm 415. Housings 420and 425 may contain various electronics including a microprocessor,interfaces, one or more wireless transceivers, a battery, a camera, aspeaker, etc. Although FIGS. 4A and 4B illustrate a monocularembodiment, head wearable display 400 may also be implemented as abinocular display with two eyepieces 401 each aligned with a respectiveeye of the user when display 400 is worn.

The see-through piece 401 is secured into an eye glass arrangement orhead wearable display that can be worn on the head of a user. The leftand right ear arms 410 and 415 rest over the user's ears while nosebridge 405 rests over the user's nose. The frame assembly is shaped andsized to position viewing region 147 in front of an eye of the user.Other frame assemblies having other shapes may be used (e.g.,traditional eyeglasses frame, a single contiguous headset member, aheadband, goggles type eyewear, etc.).

The illustrated embodiment of head wearable display 400 is capable ofdisplaying an augmented reality to the user. See-through eyepiece 401permits the user to see a real world image via external scene light 170.Left and right (binocular embodiment) display light 180 may be generatedby display sources 120 mounted in peripheral corners outside the user'scentral vision. Display light 180 is seen by the user as a virtual imagesuperimposed over external scene light 170 as an augmented reality. Insome embodiments, external scene light 170 may be fully, partially, orselectively blocked to provide sun shading characteristics and increasethe contrast of image light 180 via tinting add-on component 110.

The above description of illustrated embodiments of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various modifications arepossible within the scope of the invention, as those skilled in therelevant art will recognize.

These modifications can be made to the invention in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the invention to the specific embodimentsdisclosed in the specification. Rather, the scope of the invention is tobe determined entirely by the following claims, which are to beconstrued in accordance with established doctrines of claiminterpretation.

What is claimed is:
 1. An eyepiece for a head wearable display, theeyepiece comprising: a light guide component for receiving display lightat a peripheral location and emitting the display light at a viewingregion, the light guide component including: an eye-ward facing surfacehaving a reflection portion and a viewing portion; a folding surfaceopposing the eye-ward facing surface, the folding surface oriented toreflect the display light received into the light guide component to thereflection portion of the eye-ward facing surface; and a first interfacesurface disposed opposing the eye-ward facing surface in the viewingregion and oriented to receive the display light reflected from thereflection portion of the eye-ward facing surface; and a partiallyreflective layer disposed on the first interface surface in the viewingregion, the partially reflective layer to reflect the display lightthrough the viewing portion of the eye-ward facing surface.
 2. Theeyepiece of claim 1, wherein the partially reflective layer comprises abeam splitter or polarizing beam splitter that partially reflects thedisplay light.
 3. The eyepiece of claim 1, further comprising: asee-through add-on component mounted to the light guide component alongthe first interface surface in the viewing region, wherein the partiallyreflective layer is disposed in the viewing region at an interfacebetween the first interface surface of the light guide component and thesee-through add-on component, wherein the see-through add-on componentand the viewing region of the light guide component are at leastpartially transparent to external scene light.
 4. The eyepiece of claim3, wherein the see-through add-on component is formed of a materialhaving an index of refraction substantially equivalent to that of thelight guide component.
 5. The eyepiece of claim 3, wherein thesee-through add-on component comprises: a second interface surfacehaving a size and curvature that mates to the first interface surface ofthe light guide component; and an external scene facing surface having afirst curvature that is complementary to a second curvature of theeye-ward facing surface in the viewing region to substantially offsetoptical power of the eye-ward facing surface in the viewing region. 6.The eyepiece of claim 5, wherein the first curvature of the externalscene facing surface of the eye-through add-on component forms acontinuous surface with the folding surface of the light guidecomponent.
 7. The eyepiece of claim 1, wherein the reflection portion ofthe eye-ward facing surface and the folding surface are clear surfacesthat are oriented to reflect the display light via total internalreflection.
 8. The eyepiece of claim 1, further comprising: an inputsurface oriented to receive the display light into the light guidecomponent at the peripheral location, wherein the input surface is adistinct and separate surface from the eye-ward facing surface.
 9. Theeyepiece of claim 8, wherein the folding surface, the eye-ward facingsurface, and the first interface surface are all curved surfaces shapedto impart optical power in reflection on the display light and whereinthe light guide component has a rectangular cross-sectional shape. 10.The eyepiece of claim 9, wherein the light guide component magnifies thedisplay light emitted out the viewing region relative to the displaylight received at the peripheral location.
 11. The eyepiece of claim 1,wherein the folding surface and at least the reflection portion of theeye-ward facing surface are coated with an anti-fingerprint coating. 12.The eyepiece of claim 1, wherein the light guide component displays animage plane that is flatter than 0.1 diopters.
 13. A head wearabledisplay for displaying an image, the head wearable display comprising: adisplay source to generate display light; a see-through eyepieceincluding: a light guide component for guiding the display lightreceived at a peripheral location and emitting the display light at aviewing region, the light guide component including an eye-ward facingsurface having a reflection portion and a viewing portion, a foldingsurface oriented to reflect the display light to the reflection portionof the eye-ward facing surface, and a first interface surface disposedin the viewing region; a see-through add-on component mounted to thelight guide component along the first interface surface in the viewingregion; and a partially reflective layer disposed at the first interfacesurface in the viewing region, the partially reflective layer to reflectthe display light through the viewing portion of the eye-ward facingsurface; and a frame assembly to support the see-through eyepiece andthe display source for wearing on a head.
 14. The head wearable displayof claim 13, wherein the partially reflective layer comprises a beamsplitter or polarizing beam splitter that partially reflects the displaylight.
 15. The head wearable display of claim 13, wherein thesee-through add-on component is formed of a material having an index ofrefraction substantially equivalent to that of the light guidecomponent.
 16. The head wearable display of claim 13, wherein thesee-through add-on component comprises: a second interface surfacehaving a size and curvature that mates to the first interface surface ofthe light guide component; and an external scene facing surface having afirst curvature that is complementary to a second curvature of theeye-ward facing surface in the viewing region to substantially offsetoptical power of the eye-ward facing surface in the viewing region. 17.The head wearable display of claim 13, wherein the reflection portion ofthe eye-ward facing surface and the folding surface are clear surfacesthat are oriented to reflect the display light via total internalreflection.
 18. The head wearable display of claim 13, wherein thefolding surface, the eye-ward facing surface, and the first interfacesurface are all curved surfaces shaped to impart optical power inreflection on the display light.
 19. The head wearable display of claim13, wherein the light guide component and the see-through add-oncomponent both have a rectangular cross-sectional shape.
 20. The headwearable display of claim 13, wherein the folding surface and at leastthe reflection portion of the eye-ward facing surface are coated with ananti-fingerprint coating.